1. Field of the Invention
The present invention generally relates to a distance measuring technology. More particularly, the present invention relates to an apparatus and method for tracking a fixed target without using equipment such as a plurality of fixed reference nodes by a mobile system under an indoor wireless environment.
2. Description of the Related Art
Ubiquitous computing is a concept of building a space in which all entities and objects are intellectualized, connected to an electronic space, and are able to exchange information with one another by adding a computing function to every physical space and object including roads, bridges, tunnels, buildings, building walls, etc.
The basic premise upon which ubiquitous computing was founded is that all computers are connected to one another, are available to users at any time in any place, though invisible to the users, and are integrated into their daily livings in a real world. A core infrastructure to realize this ubiquitous environment, ubiquitous network is an information communication network that is accessible to anyone irrespective of time and place without any constraints of communication speed or the like and can distribute every information and content.
Owing to the realization of the ubiquitous network, users can expect to enjoy information communication services freely without many limitations encountered with legacy information communication networks and services. Especially, for example, a community that goes beyond time and space can be formed by use of the ubiquitous network and various sensors and the contexts and locations of people and objects can be known through the community.
The proliferation of ubiquitous computing and the ubiquitous network will create new, diverse services that may include a ubiquitous location-based application service for locating persons and objects anytime anywhere. The provision of such a useful service based on the locations of people and objects is emerging as a significant factor in further developing the ubiquitous environment.
Location awareness technology for acquiring information about the current location of a user is a basic technology that is a priority in terms of support in order to realize the ubiquitous computing that autonomously recognizes the situation of a user anytime anywhere, and provides a service suitable for the situation to the user. Active research is underway on the location awareness technology in many countries.
For location awareness, there are a Global Positioning System (GPS)—or mobile communication Base Station (BS)-based tracking technology, a location referencing technology using milestones, spots, directions, distances, etc. and a numerical map technology based on topology, scale conversion, or format conversion. However, these location awareness technologies have a shortcoming in that they were developed for outdoor use, and thus are not applicable to an indoor environment for accurate positioning. Accordingly, location awareness technologies have been developed separately for location awareness in an indoor environment.
An indoor location system, such as a wireless communication, infrared, or ultrasonic, requires installation of a predetermined number of fixed reference nodes. The reference nodes have absolute coordinates or relative coordinates with respect to a single node, and are preliminarily entered in order to determine the relative coordinates of a target mobile tag node. The coordinates of the mobile tag node are calculated using distances measured by bi-directional communications between the mobile tag node and the fixed reference nodes. Each node in the system has its specific clock value, a transmission time is estimated by exchanging the specific values, and then the distance between nodes is measured using a transmission time in the wireless communication, infrared, or ultrasonic location system.
FIG. 1 illustrates a conventional method for tracking the location of a target object indoors by infrared rays. Referring to FIG. 1, magnetic north (N) is determined using a magnetic sensor, or an electronic compass, and the azimuth angle between a target and the magnetic north is determined using a rotational antenna or rotating infrared beams. Then the distance (d) between a location tracking apparatus and the target is determined by measuring the Time of Arrival (ToA) of a signal at the target or measuring the Received Signal Strength (RSS) of a signal received from the target. The target is tracked down in the shorted route based on the azimuth angle and the distance.
However, there are problems associated with the above tracking method, which typically tracks a target using infrared rays, ultrasonic waves, or electromagnetic waves, as it suffers from interference due to ambient sun rays or a nearby light in the case of infrared distance measurement, a long time delay in the case of an ultrasonic technology, and a distance measurement accuracy of 3 m or longer (i.e. difficulties in accurate distance measurement in the case of electromagnetic-based RSS detection).
Moreover, the conventional indoor location system has a higher installation costs because of the requirement of a plurality of fixed reference nodes, a sensor system, and a server system for indoor positioning. The conventional target tracking system also has the disadvantages of the use of large amounts of equipment for everyday operation. Moreover, the higher costs further include costs for a phase array antenna or a motor-rotated antenna to acquire information about the distance and azimuth angle between a location tracking apparatus because the conventional receives angle information through phase-array or motor-rotated antenna. In addition a target and the need for a magnetic sensor or an accurate compass to obtain information about a reference direction further complicates installation and increases associated costs.
Tracking the location of a target in the conventional systems is also limited to a very confined area or takes a lot of equipment and cost. Accordingly, there exists a need for tracking a fixed target using minimum system resources in an indoor environment.